The invention relates to a protective helmet with an outer shell and an inner shell, according to the precharacterizing clause of Patent claim 1.
In order to prevent or reduce skull and brain injuries, it is customary to make use of protective helmets in various situations. Many different types of protective helmet, with different designs and characteristics, are available on the market. Generally speaking, such a helmet consists of a hard outer shell, often made of a composite material, and an energy-absorbing inner shell. Nowadays, a protective helmet has to be designed so as to satisfy certain legal requirements which relate to inter alia the maximum acceleration that may occur in the center of gravity of the brain at a specified load. Typically, tests are performed, in which what is known as a dummy skull equipped with a helmet is subjected to a radial blow from an impact surface. This has resulted in modern helmets having good energy-absorption capacity in the case of blows radially against the skull while the energy absorption for other load directions is not as optimal. The absence of legal requirements for how helmets are to reduce angular acceleration is due to inter alia the fact that injury criteria for rotational injuries are lacking.
In the case of linear acceleration (linear impact), it is typically fractures of the skull and/or pressure or abrasion injuries of the brain tissue which occur. Instances of pure angular acceleration (rotation about the center of rotation of the. skull) are rare. The commonest type of acceleration is rotational acceleration, that is to say combined linear and angular acceleration. Examples of rotational injuries are on the one hand subdural haematomas, SH, bleeding as a consequence of blood vessels rupturing, and on the other hand diffuse axonal injuries, DAI, which can be summarized as nerve fibres being severed as a consequence of varying inertia and density in the tissues of the brain. Depending on the characteristics of the rotational force, such as the duration, amplitude and rate of increase, either SH or DAI occur, or a combination of these is suffered. Generally speaking, SH occur in the case of short duration and great amplitude, while DAI occur in the case of longer and more widespread acceleration loads. It is important that these phenomena are taken into account so as to make it possible to provide good protection for the skull and brain.
The aim of the invention is to produce a protective helmet which reduces the risk of injury for the wearer. Another aim is to produce a protective helmet which is simple, light and flexible for the wearer. A further aim is to produce an easily manufactured protective helmet.
An effective protective helmet is obtained with an embodiment which has features according to the characterizing clause of Patent claim 1.
By virtue of the fact that the outer shell of the helmet can be displaced relative to the inner shell during simultaneous absorption of rotational energy in the helmet, it is possible to reduce the injurious forces acting on the wearer, with a reduced risk of injury as a consequence.
The use of one or more relatively thin sliding layers means that the mass and construction height of the helmet can be kept down, which increases wearer comfort and further reduces the risk of injury.
By using an inner shell with the currently customary characteristics for protective helmets, a protective helmet is obtained, which is well suited to absorbing both radial impacts and oblique impacts and can thus protect the wearer well.
Further features and advantageous characteristics emerge from the description and patent claims below.